Tunable electrical circuits



Jime- 14, 1949. I sT u AL 2,473,310'

TUNABLE ELECTRICAL CIRCUITS Filed April l4, .1943

JOHANNES MARINUS VAN HOFWEEGEN I & MAXIMILIAAN JULIUS OTTO STRUTT I NVENTORS ATTORNEY ferent values.

Patented June 14, 1949 EEECTRIGAD GIRCUIT'S wMaximilia-anwdnlius- Otto .wStrutt and, Johannes Marinus van IHofweegem v.Eindhoven, ..Netherlands, assignorstoHal-tforil National Bank and Trust Company, Hartford, Conn., as trustee Applicatiorr April 314, 1943,:Serial1 No. 483,004 lln the Netherlands May 23,-1941 Section -1, *Publio Law 690; "August "8,- 1946 Patent expires May '23,"-1961 -13 Claims.

- .1 For ultra-short" wave purposes use'is-irequently made of oscillatory circuits which substantially consist of a system of two parallel--rconductors, which conductors either are placed. side by "side oragain are formed as. concentric conductors.

- For alteringthe tuning sfrequency of-such oscillatory circuits it is:known;to utilize a tuning bridgewhich is-slidable along the-conductor system :and which :iorms a short-circuit for oscillationsziwhosegfrequency corresponds to the natural frequency ofqthe-rsystemc :The :movement of the tuning bridge pisxpreferably .efiected 1 in this case 1 bymeansxof azthreaded shaft.

.' Itthasa-been;ound,: however, that it is difficult to tune these' known tunableoscillatorycircuits' .very exactly for very 'short'waves, for; example,

iftheswave length is ofzthe Orderofmagnitude of .10 ems. sinceeven a very. slight .,:displacement of the-tuning ibridge, forexample a: displacement great variation of the tuning frequency. :As a result,- :great practicalinconveniencesrare encountered in the mechanical constructions of-wt'he tuning rmechanism.

. These drawbacks :mayibe obviated by ;nti lizing, v in accordance. with the :invention, .anroscillatory circuit Jwhich comprises two .tbridg-ecpi'eces of which. at least. onerisaslidable along; the conductor system: whilst the two bridge :pieces are @conpled with a common tuning member -and, iwhen-.1the

latter is being operated;aresmovedwith respect to the :tuning member in the. longitudinal-direction oftheiconductcr system in:.the same direction. and at different: speeds.

. .The tuning member preferably..comprises a shaft .which exhibits. two :threaded partsboth of which are mechanically coupled .withi the vtuning bridges respectively and have screwethneads whose pitches have the same direction but dif- "When the invention is carried into e'fiect the 'lengthof that part of therconductor systemwhich determines thematural ;frequency or. the circuit,

undergoes .a change which corresponds to the disparity. in displacement of the two bridgepieces with respect to-the tuning member? The manufacture of 1 the tuning -mechanism, fon -exlarge pitch, does not-entail grave practicalmconveniences whilst a' sufiicient -accuracy-"of" tuning may'be' ensured in :the caseofer-y short waves, for -example of 10cms.

, The-invention will be explained moreifull-y with .reference:= to the accompanying drawing which I ofabout 0.01'mm; brings-about a comparatively 0 uzepresents byxway of example, two forms of con- ;struction ;ofytunable oscillatory-circuits accordto '.the invention.

1" 1 :represents an oscillatory circuit accordving ate the invention which substantially consists wofxatwo conductors arranged side by sidevand .-:parallel to one;another, whilst i'Figpz representsan oscillatory circuitaccordlingoto. the invention which comprises two: con- -:centric. conductors.

In Fig. 1, I and 2 denote conductorsvwhichvare arranged side by :side and parallel to;:one anotheruandwhich, .jointlywith bridge :pieces 3 "and 4; form :an oscillatory circuit. The brid pieces '3 and 4 areslidable with respect to rthe conductors l and land vmaybe displaced-with 'theaid of .-a tuning shaft .5 :provided'with an operating knob 5. "The coupling of the :oscillatory :circuit with the other elements ofzthe'icircuitarrangement in.which-.the oscillatory circuit :is utilized,.ma-y be brought about, for example; 'by means of a coupling loop :9 providedwithmconheating-terminals: It, said loop being ,astationary with-respectto the conductors i and 12.

' The tuning shaft comprises two threaded parts IT and 98 of substantially equal length which, when the .knobt is being turned, move .thebridgeupieces 3-and L4 respectivelywith respect to the conductors; The-pitches ofthe screw;:threads I and 8 'have the same direction but .difier'ent ---values.so that the relative displacement oft-the bridge-pieces and therefore :the variation oftthe -natural frequency of the oscillatory circuitis'de- --termined--by the difference in valuebetween the "pitch of the screw thread 1 and that of -the screw thread BHThe screw thread i exhibits, for example, -nine'and the :screw thread 8 ten threads per-cm in which event upon lten revolutions of theoper- 'ating-- knob==thechange in length of the-'osci11atory circuit conductors is only about Lmmz-and consequently withvery short Waves an exact tuning-can-be ensured without practical drawbacks --bing-encountered in the production of -the screw "thread.

' In order to preventthe--oscillatory circuit'irom 'bein influenced by the tuning shaft, the latter i-s -pre'ferably made of insulating material.

In order to avoid back lash of the "tuning mechanisnr due to the play which-maypccur-between-"the screw threads 1, 8 andthe -briclge-pieces 3, aye: is-advantageous to utilize means'known @1361 se in order to avoid-such aplay. For-=this purpose use-"maybemade, for-example, of helical s/pri-ngs which aresecuredat one endto-the shaft and-at the other endto a 'bridge piece and which thus exert on the latter a force which is axially directed.

In the above it is tacitly assumed that the two bridge-pieces are slidable with respect to the conductor system and that the shaft 5 cannot be displaced in the longitudinal direction of the conductors. It is, however, also possible to arrange that one of the two bridge pieces and the shaft 5 are slidable with respect to the fixed conductors l, 2 without departing from the essence of the present invention as will be set out more fully with reference to Fig. 2.

The oscillatory circuit according to Fig. 2 comprises two concentric conductors H and i2 whilst at the two ends are provided bridge-pieces l3 and M. The bridge-piece 113, which galvanically connects the conductors to one another at one end, is rigidly connected to the conductors and preferably has a circular shape so that the space between the conductors is closed. The bridgepiece It is mounted so as to be slidable with respect to the conductors and exhibits a circular hole through which passes the inner conductor I2 whilst the outer circumference preferably also has a circular shape. In order to ensure a satisfactory contact along the whole inner and outer circumferences of the bridge-piece M with the conductors, it is advantageous, as it is known in itself, to utilize resilient contact strips which are provided on the inner and outer circumference respectively.

At the end remote from the bridge-piece t3 the space between the conductors is closed by a circular plate but which plate may also be omitted as one versed in the art can readily appreciate from the Fig. 1 embodiment of this invention.

The outer conductor H, which, in the form of construction according to Fig. 2 acts at the same time as a screening envelope, is provided with two slots I6, I! which are provided diametrically opposite one another and which extend in the axial direction of the conductors. Two projections of the tuning bridge Hi project through the said slots to the outside. The slots serve to guide the bridge-piece and prevents the latter from rctating. To the projections of the bridge I4 are secured the ends of two rods :18 and i9, preferably of insulating material, which are symmetrically arranged with respect to the oscillatory circuit and which are secured at the other ends to a transverse connecting piece 20 which is provided with a threaded hole. This screw thread corresponds to that part of a tuning shaft 22 which has a screw thread 2!, said shaft being provided with an operating knob 23 with the aid of which the bridge-piece M may be displaced with respect to the conductors l l l2. Owing to the symmetrical construction of the tuning mechanism any torsion of the bridge 14 in the outer conductor when the latter is being displaced is avoided.

By turning the tuning shaft 22 the bridgepiece It is moved relatively to the said shaft. However, by turning the shaft 22, the latter is also displaced in its longitudinal direction relatively to the oscillatory circuit H, 112 with the aid of a second part of the shaft, which part is provided with a screw thread 2% and is journalled in a part of the hollow inner conductor 12 which is provided with a screw thread 25.

Since here again the pitches of the screw threads 21 and 24 have the same direction but different values, the displacement of the tuning bridge l4 relatively to the conductors H and I2 is determined, as in Fig. 1, by the disparity in relative displacement of the parts 54 and 22 and the parts 22 and I2 respectively, owing to which exact tuning of the oscillatory circuit is ensured.

In the forms of construction represented by way of example, the length of the conductor system corresponds to one-half wavelength of oscillations with a natural frequency of the circuit, which in itself is advantageous with very slight wavelengths since in this case the length of the oscillatory circuit conductors does not become too small.

Upon carrying out the invention for wavelengths with which from a mechanical point of view the slightest possible length of the conductor system is allowable, the length of each of the oscillatory circuit conductors preferably corresponds to'a quarter wavelength. When the invention is carried into effect, one of the bridgepieces should consist in this case of insulating material and exclusively forms of construction fundamentally similar to that of Fig. 2 may, of course be utilized.

We claim:

1. A tunable oscillatory circuit comprising an inner and an outer conductor fixedly connected together at one end by an end plate so as to constitute a concentric line resonator, a metallic bridge piece connecting the outer surface of the inner conductor with the inner surface of the outer conductor for tuning said oscillatory circuit, a shaft having two spaced screw threads of different pitches, said shaft entering the interior of said inner conductor, one of said screw threads engaging said inner conductor for causing movement of said concentric line resonator as an integral unit, the other of said screw threads on said shaft being linked to said bridge piece, whereby rotation of said shaft causes both said resonator and said bridge piece to move simultaneously in the same direction but at different rates.

2. A tunable oscillatory circuit comprising an inner conductor with an interiorly threaded end, an outer conductor with opposed slots concentric with said inner conductor, means fixedly coupling said conductors respectively at each end to produce a resonator, movable bridge means with projections mating said slots for connecting and guiding the outer surface of the inner conductor with the outer conductor for tuning said oscillatory circuit, a centrally located transversely threaded connecting piece, rod means coupling said movable bridge means with said connecting piece, a shaft with spaced groups of threads of different pitches threaded into said connecting piece and said inner conductor whereby rotational movement of said shaft causes relative motion between said resonator and said bridge means.

3. A tunable oscillatory circuit comprising an inner and an outer conductor fixedly connected together at one end by an end plate and at the other end by a first bridge piece so as to constitute a concentric line resonator, a second metallic bridge piece connecting the outer surface of the inner conductor with the inner surface of the outer conductor for tuning said oscillatory circuit, a shaft having two spaced screw threads of difierent pitches, said shaft entering the interior of said inner conductor, one of said screw threads engaging said inner conductor for causing movement of said concentric line resonator as an integral unit, the other of said screw threads r on said shaft being linked to said second bridge -piece,-whereby rotation of said shaft causes both said resonator and said. second bridge piece to move simultaneously in the same direction but UNITED STATES PATENTS Number Name Date at dlfierem rates- 2,019,809 Carter Nov, 5, 1935 2,117,090 Grundmann Ma 10, 1938 JOHANNES MARINUS VAN HOFWEEGEN. 5 2 231 152 Buschbeck 11 1941 MAXIMILIAAN JULIUS OTTO STRUTT. 2397737 Gubin Apr 1946 REFERENCES CITED FOREIGN PATENTS The following references are of record in the Number Country Date file of this patent: 244,009

Great Britain Dec. 10, 1925 

